Estimation of mud filtrate spectra and use in fluid analysis

Abstract

A method for using an optical spectrum of mud filtrate for analysis of fluid drawn from a formation is provided. The method includes performing downhole fluid analysis of formation fluid drawn at a wellbore measurement station and determining an optical spectrum of mud filtrate in the formation fluid drawn at the wellbore measurement station. The method also includes performing downhole fluid analysis of formation fluid drawn at an additional wellbore measurement station, and performing the downhole fluid analysis of formation fluid drawn at the additional wellbore measurement station includes using the determined optical spectrum of the mud filtrate in the formation fluid previously drawn at the wellbore measurement station. Additional methods, systems, and devices are also disclosed.

The invention claimed is: 
     
       1. A method comprising:
 performing downhole fluid analysis of formation fluid drawn at a wellbore measurement station; 
 determining a characteristic of mud filtrate in the formation fluid drawn at the wellbore measurement station; and 
 performing downhole fluid analysis of formation fluid drawn at an additional wellbore measurement station, wherein performing the downhole fluid analysis of formation fluid drawn at the additional wellbore measurement station includes using the determined characteristic of the mud filtrate in the formation fluid drawn at the wellbore measurement station, wherein (1) the wellbore measurement station is in a water zone of a well and the additional wellbore measurement station is in an oil zone of the well, or (2) the wellbore measurement station and the additional wellbore measurement station are in different wells. 
 
     
     
       2. The method of  claim 1 , wherein determining the characteristic of the mud filtrate includes determining at least one of an optical spectrum, density, viscosity, compressibility, or composition of the mud filtrate. 
     
     
       3. A method comprising:
 performing downhole fluid analysis of formation fluid drawn at a wellbore measurement station; 
 determining an optical spectrum of mud filtrate in the formation fluid drawn at the wellbore measurement station; 
 calibrating an optical fluid analyzer using the determined optical spectrum of the mud filtrate in the formation fluid drawn at the wellbore measurement station; and 
 using the calibrated optical fluid analyzer to measure an optical spectrum of the formation fluid drawn at an additional wellbore measurement station; 
 identifying or determining contamination of a hydrocarbon fluid in the formation fluid drawn at the additional wellbore measurement station. 
 
     
     
       4. A method comprising:
 measuring, with a downhole tool positioned within a wellbore, a plurality of sets of optical densities of formation fluid to multiple wavelengths of electromagnetic radiation; 
 calibrating the downhole tool within the wellbore based on the plurality of sets of measured optical densities, including filtering the compared sets or determining a representative mud filtrate spectrum from the compared sets and using the determined representative mud filtrate spectrum to calibrate the downhole tool; and 
 measuring, with the calibrated downhole tool, an additional set of optical densities of formation fluid to multiple wavelengths of electromagnetic radiation. 
 
     
     
       5. The method of  claim 4 , wherein calibrating the downhole tool within the wellbore based on the plurality of sets of measured optical densities includes comparing at least some sets of the plurality of sets to one another. 
     
     
       6. A method comprising:
 performing downhole fluid analysis of formation fluid drawn at a wellbore measurement station; 
 determining a characteristic of mud filtrate in the formation fluid drawn at the wellbore measurement station; 
 performing downhole fluid analysis of formation fluid drawn at an additional wellbore measurement station, wherein performing the downhole fluid analysis of formation fluid drawn at the additional wellbore measurement station includes using the determined characteristic of the mud filtrate in the formation fluid drawn at the wellbore measurement station; and 
 extrapolating a mud filtrate optical spectrum of the formation fluid drawn at the additional wellbore measurement station from the determined optical spectra mud filtrate in the formation fluid drawn at the additional wellbore measurement station. 
 
     
     
       7. The method of  claim 6 , comprising:
 performing downhole fluid analysis of formation fluids drawn at a plurality of wellbore measurement stations; and 
 determining optical spectra of mud filtrate in the formation fluids drawn at the plurality of wellbore measurement stations. 
 
     
     
       8. The method of  claim 7 , comprising extrapolating a mud filtrate optical spectrum of the formation fluid drawn at the additional wellbore measurement station from the determined optical spectra of mud filtrate in the formation fluids drawn at the plurality of wellbore measurement stations. 
     
     
       9. The method of  claim 8 , wherein extrapolating the mud filtrate optical spectrum of the formation fluid drawn at the additional wellbore measurement station includes filtering the determined optical spectra of mud filtrate in the formation fluids drawn at the plurality of wellbore measurement stations and estimating the mud filtrate optical spectrum of the formation fluid drawn at the additional wellbore measurement station from the filtered optical spectra. 
     
     
       10. The method of  claim 7 , comprising using the determined optical spectra of mud filtrate in the formation fluids drawn at the plurality of wellbore measurement stations to calibrate a sensor of a downhole tool.